Effects of negative substrate bias voltage on the structure and properties of aluminum oxide films prepared by DC reactive magnetron sputtering

► Effects of Vb on as-deposited, annealed and heated AlxOy films are studied. ► The crystallization intensity of heated films gets weaker with increasing Vb. ► Grain refinement for as-deposited films and crack surface for annealed are found. ► Films after annealing exhibit higher transmittance but lower microhardness.